I tried PhotoJPEG, JPEG 2000, PNG, ANIMATION all with same problem (all compressions generated in QuickTime pro)
I even have the problem when I render a straight uncompressed quicktime out of after effects.
But when I open my H264 in WindowsMediaPlayer or in AE, everything seems fine, it seems the problem comes from quicktime pro (definitly not from my hard drive speed or hardware since I have a modern gear). Really dont get it, how come WMP perform better than QUickTime and if the biterate is quite low then what is causing this in my quicktime pro player?